Optical element and optical system having the same

ABSTRACT

An optical element formed from a transparent optical material includes two refraction surfaces, a first reflection surface group having a plurality of internal reflection surfaces arrayed in a predetermined direction, a second reflection surface group opposing the first reflection surface group and having at least one internal reflection surface and two side surfaces opposing each other in parallel to the predetermined direction. Light incident from one of the refraction surfaces is alternately reflected by the internal reflection surfaces of the first reflection surface group and the internal reflection surface of the second reflection surface group and guided to the other refraction surface. The width of at least one of the plurality of internal reflection surfaces of the first reflection surface group and at least one internal reflection surface of the second reflection surface group in a direction in which the two side surfaces oppose each other is smaller than the distance between the two side surfaces in the direction in which the side surfaces oppose each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical element and an opticalsystem using the same and, more particularly, to an optical system for avideo camera, still video camera viewfinder, or a copying machine usingan optical element integrating a plurality of reflection surfaces withcurvatures.

2. Related Background Art

Conventionally, a variety of optical systems using the reflectionsurfaces of concave mirrors or convex mirrors have been proposed.

For example, U.S. Pat. No. 4,775,217 or Japanese Patent ApplicationLaid-Open No. 2-297516 discloses an optical prism whose optical blockhas a reflection surface with a curvature.

U.S. Pat. No. 4,775,217 is associated with the arrangement of theeyepiece of an observation optical system. FIG. 11 shows thisarrangement.

In the observation optical system shown in FIG. 11, display light 215from an information display 211 is incident from an incident surface218, is reflected to the object side by a total reflection surface 212,and reaches a concave surface 213 having a curvature.

The display light 215 that is output from the information display 211 asdivergent light is converted into almost collimated light by the powerof the concave surface 213 and enters a pupil 214 of the observerthrough the total reflection surface 212, so the observer recognizes theimage displayed on the information display 211.

In this prior art, the object image can also be recognizedsimultaneously with observation of the displayed image.

Object light 216 is incident on a surface 217 nearly parallel to thetotal reflection surface 212 and reaches the concave surface 213. Forexample, a semi-transparent film is deposited on the concave surface213. The object light 216 half-transmitted through the concave surface213 passes through the total reflection surface 212 and enters the pupil214 of the observer. Hence, the observer can observe the object light216 and the display light 215 in a superposed state.

In a non-coaxial optical system, when asymmetrical aspherical surfacesare formed as constituent surfaces on the basis of the idea of areference axis (to be described later), a compact observation opticalsystem whose aberration is sufficiently corrected can be constructed.Japanese Patent Application Laid-Open No. 9-5650 discloses a method ofdesigning the optical system. Japanese Patent Application Laid-Open Nos.8-292371 and 8-292372 disclose examples of design.

Such a non-coaxial optical system is called an off-axial optical system(An off-axial optical system is defined as an optical system includingsurfaces (off-axial optical surfaces) whose surface normals at theintersections between the surfaces and a reference axis are not presenton the reference axis which is along a light beam passing through theimage center and the pupil center. At this time, the reference axisbends).

In this off-axial optical system, generally, the constituent surfacesare non-coaxial, and the reflection surfaces do not generate an eclipse.For this reason, an optical system using reflection surfaces can beeasily constructed. In addition, an integrated optical system can beeasily constructed by integrally molding the constituent surfaces. Withthis method, the optical path can be relatively freely guided.

Hence, a compact reflection optical element with a high space efficiencyand free shape can be formed.

However, in the integrally molded optical block of the off-axial opticalsystem, when the number of reflection surfaces is increased for thepurpose of, e.g., aberration correction of the optical block, influencesof surface shape errors or surface distortion as manufacturing errors ofthe reflection surfaces accumulate. The error amount allowable in eachreflection surface becomes smaller and stricter as the number ofreflection surfaces increases. For this reason, the surface shape ofeach reflection surface must be accurately guaranteed.

An optical system with a small image size, which is disclosed in, e.g.,Japanese Patent Application Laid-Open No. 8-292371 or 8-292372, haslarge curvatures, and the required accuracy against surface errors orsurface distortion is high.

This also applies to the observation optical system disclosed in U.S.Pat. No. 4,775,217 or Japanese Patent Application Laid-Open No. 2-297516when a compact high-performance optical system is constructed.

The characteristic features of the reflection optical elements disclosedin Japanese Patent Application Laid-Open Nos. 8-292371 and 8-292372 willbe described next.

FIG. 12 shows an embodiment disclosed in Japanese Patent ApplicationLaid-Open No. 8-292371. This optical system has an intermediate imagingplane N1 and a pupil N2 of the optical system. The intermediate imagingplane is formed near a second reflection surface R4 counted from anincident surface R2 along the optical path, i.e., one of reflectionsurfaces having curvatures.

The pupil is formed near a second reflection surface R6 reverselycounted from the exit surface along the optical path, i.e., one of thereflection surfaces having curvatures. If a first reflection surface R3having a curvature, which is counted from the incident surface R2 alongthe optical path, has a convergence function, the intermediate imagingplane N1 readily forms near the above-described reflection surface R4.If a final reflection surface R7 having a curvature, which is countedfrom the incident surface along the optical path, has a convergencefunction, the pupil N2 readily forms near the above-described reflectionsurface R6.

These surfaces are sensitive to distortion and spherical aberration, sothe surface shapes must be accurately guaranteed.

To form an optical block having a plurality of reflection surfaces,molding using a mold is widely used because of the recent requirementfor simplicity. When the mold is larger than the optical effectiveportion to some extent, the influence of the surface distortion near thereflection surfaces on the optical effective portion becomes small.

A large mold is also advantageous in guaranteeing the positionalaccuracy of each reflection surface. In a process using a syntheticresin, changes in dimensions due to shrinkage in the molding or the useenvironment must be taken into consideration because the thermalexpansion coefficient of the synthetic resin is larger than that of aninorganic material by one order of magnitude. In association with theoptical characteristics, not only the molding accuracy but also moldingshrinkage and molecular orientation need to be taken into consideration.

Molding shrinkage influences the dimension accuracy of the entire moldedbody. Local shrinkage in cooling appears as residual distortion ordeformation. Generally, when a molding material hardens in a mold,shrinking stress remains because the material cannot freely shrink. Whena molded body formed from a soft material is released from a mold, suchstress is released to warp the molded body. For a hard material such aspolystyrene, polymethyl methacrylate, or polycarbonate, stress is notreleased, and a molded body maintains its shape with residual stress.

This stress is called internal stress. When the molded body comes intocontact with, e.g., a solvent, a crack readily forms. The molded bodymay spontaneously break during use.

In consideration of this problem, Japanese Patent Application Laid-OpenNo. 8-122505 discloses an examination in which when a plurality ofoptical components are to be integrally formed as one optical member,contact surfaces at a joint portion are formed into appropriate shapes,and two surfaces adjacent to each other are smoothly joined at theboundary. This decreases residual stress on the optical member in themolding process to reduce manufacturing errors.

However, not all optical members can always be smoothly joined. When adesign is made to smoothly join an optical member, the opticalperformance cannot be maintained.

FIG. 8 is a perspective view showing the surface shapes of a reflectionoptical element disclosed in Japanese Patent Application Laid-Open No.8-292371, and the incident states of an incident light beam on thereflection surfaces. A cluster of symbols “+” represents a light beamincident on each optical surface.

FIG. 9 is a perspective view showing only the surface shapes of areflection optical element of another embodiment of this prior art.

Referring to FIG. 8, the optical element has refraction surfaces R1 andR7, reflection surfaces R2 to R6 forming two reflection surface groupsopposing each other, and an image sensing element Si such as a CCD. Alight beam from an object is incident from the incident surface R1, isrepeatedly reflected by the reflection surfaces R2 to R6, exits from theexit surface R7, and forms an image on the image sensing element Si(image sensing surface). As shown in FIG. 8, the light is incident onthe reflection surfaces in various states.

Referring to FIG. 9, the optical element has refraction surfaces R1 andR8, a reflection surface R2 which does not oppose two reflection surfacegroups opposing each other, reflection surfaces R3 to R7 forming tworeflection surface groups opposing each other, and an image sensingelement Si such as a CCD.

A light beam from an object is incident from the incident surface R1.The direction of light is changed by the reflection surface R2. Thelight beam is repeatedly reflected by the reflection surfaces R3 to R7,exits from the exit surface R8, and forms an image on the image sensingelement Si (image sensing surface).

In the example shown in FIG. 8, the curvature of the reflection surfaceR3 is large. In FIG. 9, the curvature of the reflection surface R6 islarge. The curvatures of surfaces adjacent to each other, i.e., thesurfaces R1, R3, R5, and R7 in FIG. 8 or the surfaces R4, R6, and R8 inFIG. 9 are largely different. For this reason, it is hard to smoothlyjoin these surfaces.

As is apparent from FIGS. 8 and 9, when a surface with a large curvatureis simply extended to side surfaces while maintaining the surface shapeof the optical surface, or when cross sections of adjacent surfaces withlargely different curvatures are simply joined as shown in FIG. 10, theresultant optical element has sharp ridge portions C1 on the sidesurfaces or a step at a joint portion C2 between the optical surfaces.

Generally, when reflection surfaces are larger than the opticaleffective portion to some extent, it is advantageous to guarantee thesurface accuracy of or positional accuracy of each reflection surface.In this case, an accurate surface shape can be guaranteed by ensuringthe placing of an optical reflection surface to a portion near theoptical effective portion and compensating for other portions usingshapes different from the shape of the optical reflection surface.

As shown in FIGS. 8 and 9, a surface having a large curvature and smalloptical effective portion is often convex facing the inside of thedevice.

When surfaces before and after such a surface have a convergencefunction, the optical effective portion of this surface inevitablybecomes small.

As described above, these surfaces are sensitive to distortion andspherical aberration, so the surface shapes must be accuratelyguaranteed. Generally, a molding auxiliary portion such as a draft or anejection portion formed from an ejector pin is prepared at apredetermined position of the reflection optical element, therebysuppressing manufacturing errors. To suppress manufacturing errors andguarantee the optical performance, the molding auxiliary portion ispreferably formed near a reflection surface.

An optical element represented by Japanese Patent Application Laid-OpenNo. 8-292371 aims at forming a compact and free shape. For this reason,the degree of freedom in forming a draft or an ejection portion by anejector pin is low, like conventional optical elements.

Japanese Patent Application Laid-Open Nos. 8-292371 and 8-292372disclose a means for obtaining the surface shape of the opticaleffective portion. Japanese Patent Application Laid-Open Nos. 8-292371and 8-292372 do not disclose any specific method of forming shapes otherthan the optical surface.

SUMMARY OF THE INVENTION

It is an object of the present invention to construct a reflectionoptical element having a minimum step at the boundary between an opticalsurface and a side surface or at the boundary between optical surfaces,or having a minimum surface-shape error in molding.

In order to achieve the above object, according to the first aspect ofthe present invention, there is provided an optical element formed froma transparent optical material, comprising:

two refraction surfaces;

a first reflection surface group having a plurality of internalreflection surfaces arrayed in a predetermined direction;

a second reflection surface group opposing the first reflection surfacegroup and having at least one internal reflection surface; and

two side surfaces opposing each other in parallel to the predetermineddirection,

wherein light incident from one refraction surface is alternatelyreflected by the internal reflection surfaces of the first reflectionsurface group and the internal reflection surface of the secondreflection surface group and guided to the other refraction surface, and

at least one of the plurality of internal reflection surfaces of thefirst reflection surface group and at least one internal reflectionsurface of the second reflection surface group has, in a direction inwhich the two side surfaces oppose each other, a width smaller than thedistance between the two side surfaces in the direction in which theside surfaces oppose each other.

According to the second aspect of the present invention, there isprovided an optical element formed from a transparent optical material,comprising:

two refraction surfaces;

a first reflection surface group having a plurality of internalreflection surfaces arrayed in a predetermined direction;

a second reflection surface group opposing the first reflection surfacegroup and having at least one internal reflection surface;

two side surfaces opposing each other in parallel to the predetermineddirection; and

a molding auxiliary portion provided at a portion which does notsubstantially influence optical performance,

wherein light incident from one refraction surface is alternatelyreflected by the internal reflection surfaces of the first reflectionsurface group and the internal reflection surface of the secondreflection surface group and guided to the other refraction surface.

According to the third aspect of the present invention, there isprovided an optical system comprising the optical element of the firstor second aspect of the present invention and an aperture stop.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the structure of a reflection optical elementaccording to the first embodiment of the present invention;

FIG. 2 is a view showing the structure of a reflection optical elementaccording to the second embodiment of the present invention;

FIG. 3 is a view showing the structure of a reflection optical elementaccording to the third embodiment of the present invention;

FIG. 4 is a view showing the structure of a reflection optical elementaccording to the fourth embodiment of the present invention;

FIG. 5 is a view showing part of the reflection optical elementaccording to the fourth embodiment of the present invention;

FIG. 6 is a view showing the structure of a reflection optical elementaccording to the fifth embodiment of the present invention;

FIGS. 7A and 7B are views showing the structure of a reflection opticalelement according to the sixth embodiment of the present invention;

FIG. 8 is a view showing the incident states of a light beam on aconventional reflection optical element having a prism reflectionsurface with a curvature;

FIG. 9 is a perspective view showing the optical surfaces of theconventional reflection optical element having the prism reflectionsurface with the curvature;

FIGS. 10A, 10B, and 10C are sectional views showing the conventionalreflection optical element having the prism reflection surface with thecurvature;

FIG. 11 is a view showing another conventional observation opticalsystem having a prism reflection surface with a curvature; and

FIG. 12 is a view showing the conventional optical element having theprism reflection surface with the curvature shown in FIGS. 8 and 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An optical element of the present invention has no axis of symmetry,unlike an optical axis in a normal optical system. Instead, a “referenceaxis” is set in the optical element. The arrangement of elements in theoptical element will be described on the basis of this reference axis.

First, the definition of the reference axis will be described.Generally, the optical path of a light beam with a reference wavelength,which serves as a reference from an object surface to an image plane, isdefined as the “reference axis” of the optical element. The light beamas the reference is not determined under only this condition. Normally,the reference axis light beam is set in accordance with one of thefollowing two principles.

(A-1) When an axis of symmetry is present even locally in the opticalelement, and aberration can be symmetrically corrected, a light beampassing on the axis of symmetry is set as the reference axis.

(A-2) When no axis of symmetry is present in the optical element ingeneral, or when aberration cannot be symmetrically corrected althoughan axis of symmetry is locally present, a light beam emerging from thecenter of an object surface (the center of a range to be photographed orobserved), passing through the optical element in the order ofdesignated surfaces, and then passing through the stop center, or alight beam passing through the stop center and reaching the center ofthe final image plane is set as a reference axis light beam. The opticalpath of the light beam is set as the reference axis.

Embodiments of the optical element of the present invention will bedescribed next. FIG. 1 is a schematic view showing a reflection opticalelement according to the first embodiment of the present invention.

The first embodiment has an off-axial optical system having, on surfacesof a transparent member, a plurality of curved reflection surfaces: tworeflection surface groups opposing each other (the first reflectionsurface group comprising surfaces R3, R5, and R7 and the secondreflection surface group comprising surfaces R4 and R6), and onereflection surface not opposing the reflection surface groups.

When the reflection optical element of this embodiment is to be used asan image sensing optical system, an aperture stop is disposed near anincident surface R1. An optical correction plate such as a low-passfilter (crystal plate) or an infrared cut filter is disposed near anexit surface R8 or joined to it. The image sensing surface of an imagesensing element (image sensing medium) such as a CCD is located behindthe optical correction plate.

The reference axis passes through the center of the stop and reaches thecenter of the final image plane (image sensing surface). The reflectionsurfaces R3 to R7 are formed from off-axial reflection surfaces tiltedwith respect to the reference axis.

Each of the two refraction surfaces R1 and R8 is formed from arotationally symmetric spherical or aspherical surface or a flatsurface. With this arrangement, the reference axis can be accurately setin manufacturing/evaluating the optical system.

When the reflection optical element of this embodiment is used for imagesensing, a light beam from an object is regulated in its incident lightamount by the stop. After this, the light beam is refracted by theincident surface R1 of a reflection optical element 1, reflected by thesurfaces R2 and R3, and temporarily forms an image at a position betweenthe surface R3 and the surface R4. The light beam is sequentiallyreflected by the surfaces R4, R5, R6, and R7, refracted by the exitsurface R8, and exits the surface. An object image is formed on theimage sensing surface through the optical correction plate.

Referring to FIG. 1, the two convex mirrors R4 and R6 have largercurvatures than those of the remaining surfaces. Compensation portions11 having shapes different from the reflection surfaces R4 and R6 areformed on the sides of side surfaces 12 and 13 (not shown) of thereflection surfaces R4 and R6, thereby preventing the ridge portionsbetween the reflection surfaces R4 and R6 and the side surfaces 12 and13 from becoming acute.

In the first embodiment, the width of at least one of the plurality ofreflection surfaces is smaller than the distance between the sidesurfaces.

This arrangement also prevents any large step at the boundary betweenthe reflection surfaces R4 and R6 (as is apparent from the boundarybetween the reflection surfaces R3 and R5 shown in FIG. 8 and theboundary between the reflection surfaces R4 and R6 shown in FIG. 9, thestep near the center of each reflection surface is small, but the stepbecomes larger as it is close to a side surface). This also applies tothe reflection surfaces R4 and R6 formed from concave mirrors as far asthe curvatures are large.

In the first embodiment, when two surfaces of each of the reflectionsurfaces R3, R5, and R7 have a curvature difference, a step is formed atthe boundary near the side surfaces 12 and 13. To prevent this,compensation portions are preferably formed not to make large steps. Inthe first embodiment, the compensation portions are formed from flatsurfaces. The compensation portions may be formed from curved surfaces.

In the first embodiment, both the reflection surfaces R4 and R6 havecompensation portions. However, an effect can be obtained even whencompensation portions are formed for only one reflection surface with alarger curvature.

This embodiment is not limited to the shape of the reflection opticalelement shown in FIG. 1, and any other shape can be employed.

FIG. 2 is a schematic view showing a reflection optical elementaccording to the second embodiment of the present invention. Areflection optical element 1 of the second embodiment has the samestructure as in the first embodiment except that compensation portions11 have molding auxiliary portions A and B having shapes different fromthose of surfaces R4 and R6.

The molding auxiliary portion A is the ejection portion of an ejectorpin. The molding auxiliary portion B is draft. In this reflectionoptical element 1, an intermediate imaging plane is formed near thereflection surface R4, and a pupil is formed near the reflection surfaceR6. These surfaces are sensitive to distortion and spherical aberration,and the surface shapes must be accurately guaranteed.

In the second embodiment, the molding auxiliary portions A and B areadded to the compensation portions 11 to improve the mold releasecharacteristics with respect to the mold, suppress the surface shapeerror or surface distortion in molding, and prevent degradation inaberrations such as distortion and spherical aberration.

In addition, the molding auxiliary portions A and B are added to thecompensation portions 11, and portions where the molding auxiliaryportions A and B are added need not be newly ensured. It is advantageousin forming a compact reflection optical element and increasing thedegree of freedom in selecting an optical-element shape.

In the second embodiment, the drafts B are added to the compensationportions 11 of the reflection surface R4, and the ejection portions A ofejector pins are added to the compensation portions 11 of the reflectionsurface R6. However, the present invention is not limited to this. Tominimize the manufacturing errors, molding auxiliary portions may beformed on all reflection surfaces.

In this embodiment, the types, positions, and number of moldingauxiliary portions are appropriately designed in consideration of themanufacturing method, design values, and cost.

In this embodiment, the shape of the reflection optical element is notlimited to that shown in FIG. 2. The reflection optical element can haveany other shape.

FIG. 3 is a schematic view showing a reflection optical elementaccording to the third embodiment of the present invention.

Molding auxiliary portions (drafts) B are formed on the side of allreflection surfaces of one reflection surface (R3, R5, and R7) group outof two reflection surface groups opposing each other. The shape of areflection optical element 1 is the same as in the first and secondembodiments except for the reflection surface group having the moldingauxiliary portions.

When molding auxiliary portions are formed on the side of all reflectionsurfaces of one reflection surface group, any variation in the moldrelease characteristics of the reflection surface group is suppressedand any manufacturing error can be suppressed. In the third embodiment,the molding auxiliary portion B is a draft. However, the presentinvention is not limited to this. The molding auxiliary portion B may bea curved surface smoothly joining the reflection surfaces and sidesurfaces whereby any manufacturing error can be suppressed.

FIG. 4 is a schematic view showing a reflection optical elementaccording to the fourth embodiment of the present invention.

A reflection optical element 1 of the fourth embodiment has, on surfacesof a transparent member, two reflection surface groups opposing eachother, and one reflection surface not opposing the reflection surfacegroups, as in the first embodiment. Object light is incident from arefraction surface (incident surface) R1. The direction of light ischanged 90° by a flat mirror R2. The light is repeatedly reflected by aconcave mirror R3, a convex mirror R4, a concave mirror R5, a convexmirror R6, and a concave mirror R7, and exits from a refraction surface(exit surface) R8.

Referring to FIG. 4, a joint portion a1 joins the reflection surface R2and reflection surface R4, which do not oppose each other, withoutforming any step.

In this example, the joint portion al has a flat surface and also servesas a draft.

FIG. 5 is a perspective view showing the reflection surfaces R4 and R6,the refraction surface R8, and joint portions b1 and c1. As is apparentfrom FIG. 5, the joint portion b1 has a curved surface and joins thereflection surfaces R4 and R6 without forming any step and any sharpridge, though the reflection surfaces are not smoothly joined.

The connection portion c1 has a bank shape which prevents any sharpridge portion from forming at the end portions of the reflection surfaceR6 and refraction surface R8 and reinforces the end portion of eachsurface.

In this embodiment, the joint portion a1 has a flat surface, the jointportion b1 has a curved surface, and the joint portion c1 has a bankshape. However, the present invention is not limited to this. Theshapes, positions, and number of joint portions must be appropriatelydesigned in consideration of the manufacturing method, design values,and cost.

The fourth embodiment is not limited to the shape shown in FIG. 4, andany other shape can be employed.

FIG. 6 is a schematic view showing a reflection optical elementaccording to the fifth embodiment of the present invention. The shapesof refraction surfaces and reflection surfaces of the fifth embodimentare the same as those of the optical element shown in FIG. 8. FIG. 6shows the reflection optical element viewed from an incident surface(R1) side.

In the fifth embodiment, molding auxiliary portions C and D are formedat joint portions between optical surfaces. The molding auxiliaryportion C is a draft. The molding auxiliary portion D is the ejectionportion of an ejector pin.

In a reflection optical element 1, an intermediate imaging plane and apupil are formed near two reflection surfaces R4 and R6, respectively,as in FIG. 8. These surfaces are sensitive to distortion and sphericalaberration, so the surface shapes must be accurately guaranteed.

In this embodiment, the molding auxiliary portions C and D are formed toimprove the mold release characteristics of the mold, suppress thesurface shape error or surface distortion, and prevent degradation inaberration, such as distortion or spherical aberration. When the moldingauxiliary portions C and D are formed at the joint portions, portionswhere the molding auxiliary portions need not be newly ensured. Hence, acompact reflection optical element can be formed, and the degree offreedom of shape can be increased.

In this embodiment, molding auxiliary portions E (ejection portions ofejector pins) are also formed around two refraction surfaces to improvethe mold release characteristics on the refraction surfaces.

In this embodiment, the molding auxiliary portion C has a draft, and themolding auxiliary portions D and E have the ejection portions of ejectorpins. However, the present invention is not limited to this. The types,positions, and number of molding auxiliary portions must beappropriately designed in consideration of the manufacturing method,design values, and cost.

The fifth embodiment is not limited to the shape of the optical elementshown in FIG. 6, and any other shape can be employed.

FIGS. 7A and 7B are schematic views showing a reflection optical elementaccording to the sixth embodiment of the present invention. The shapesof refraction surfaces and reflection surfaces of the sixth embodimentare the same as those of the optical element shown in FIG. 8. FIG. 7Ashows the reflection optical element viewed from an incident surface(R1) side.

When the optical effective surface of a reflection surface of thereflection optical element is present near the side surface, it isdifficult to form compensation portions on both sides of the reflectionsurface, as in the first embodiment, or add molding auxiliary portionsto the compensation portions, as in the second embodiment.

On the other hand, a light beam is not incident on the entire region ofa reflection surface, and there is a portion with minimum influence onthe optical performance, as in the reflection optical element shown inFIG. 8.

In this embodiment, molding auxiliary portions F and G are formed atportions of reflection surfaces with minimum influence on the opticalperformance.

The molding auxiliary portion F is the ejection portion of an ejectorpin, which improves the mold release characteristics of this reflectionsurface. The molding auxiliary portion G has a moderate curved surfacenear the optical effective portion which improves the mold releasecharacteristics of this reflection surface.

When the molding auxiliary portions F are formed at the joint portions,portions where the molding auxiliary portions need not be newly ensured.Hence, a compact element can be formed, and the degree of freedom ofshape can be increased.

In this embodiment, the molding auxiliary portions F have the ejectionportions of ejector pins, and the molding auxiliary portions G havemoderate curved surfaces. However, the present invention is not limitedto this. The shapes, positions, and number of joint portions must beappropriately designed in consideration of the manufacturing method,design values, and cost.

The sixth embodiment is not limited to the shape of the optical elementshown in FIG. 7, and any other shape can be employed.

In the above embodiments, one reflection optical element functions as alens unit which has desired optical performance and forms an actualimage as a whole. However, a reflection optical system having at leastone reflection optical element and constituted by a plurality of opticalblocks may be constructed.

Additionally, zooming may be realized by changing the relative positionbetween at least two reflection optical elements of the plurality ofoptical blocks.

As has been described above, a compact optical element capable of havinga free shape, and an optical system using the optical element can beprovided. In the optical element, the first reflection surface grouphaving two or more refraction surfaces and a plurality of reflectionsurfaces, which are adjacent to each other, and the second reflectionsurface group opposing the first reflection surface group and having oneor a plurality of reflection surfaces adjacent to each other, arearranged on surfaces of a transparent member. At least one of thereflection surfaces has a curvature and two side surfaces opposing eachother. A light beam is incident from one refraction surface into thetransparent member, is repeatedly reflected by the plurality ofreflection surfaces, and exits from the other refraction surface. Anobject image is observed or an object image is formed on a predeterminedsurface using the optical element having the above arrangement. Portionsother than the optical effective portion of the optical element haveshapes different from the shape of the optical surface such that thestep at the boundary between optical surfaces is minimized. In addition,molding auxiliary portions are formed at the boundary portions, therebyminimizing the surface shape error.

What is claimed is:
 1. An optical element integrally formed from atransparent optical material, comprising: two refraction surfaces; afirst reflection surface group having a plurality of internal reflectionsurfaces arrayed in a predetermined direction; a second reflectionsurface group opposing said first reflection surface group and having atleast one internal reflection surface; and two side surfaces opposingeach other in parallel to the predetermined direction, wherein lightincident from one of the refraction surfaces is alternately reflected bythe internal reflection surfaces of said first reflection surface groupand the internal reflection surface of said second reflection surfacegroup and is guided to the other refraction surface, wherein a width ofat least one of the internal reflection surfaces of said first andsecond reflection surface groups in a direction in which said two sidesurfaces oppose each other is smaller than a distance between said twoside surfaces in the direction in which said side surfaces oppose eachother, and wherein said optical element further comprises portionshaving no optical function, which are formed between said two sidesurfaces and the internal reflection surface having the width smallerthan the distance between said two side surfaces, said portions beingadjacent to the internal reflection surface having the width smallerthan the distance between said two side surfaces, and a shape of saidportions being different from that of the internal reflection surfacehaving the width smaller than the distance between said two sidesurfaces.
 2. An element according to claim 1, wherein the internalreflection surface having the width smaller than the distance betweensaid two side surfaces has a curved surface.
 3. An element according toclaim 1, wherein the internal reflection surface having the widthsmaller than the distance between said two side surfaces has a convexreflection surface.
 4. An element according to claim 1, wherein saidportions have molding auxiliary portions.
 5. An element according toclaim 4, wherein said molding auxiliary portions comprise ejectionportions of ejector pins.
 6. An element according to claim 4, whereinsaid molding auxiliary portions comprise drafts for ejecting saidoptical element from a mold.
 7. An optical system comprising: saidoptical element of claim 1; and an aperture stop.